1. Technical Field
The present disclosure relates to a microlens array, more particularly to a microlens array which is able to change optical properties by deforming the shape of a transparent dielectric polymer thin film having bistablity to various sizes of lens shapes by the purposes, and a method for fabricating thereof.
2. Background Art
Not only high resolution screens but also virtual screens or 3D images have been provided with ongoing developments in display technologies which are used for mobile terminals, projectors and TVs that are currently available. Virtual screen technology uses a projection method based on a laser light source, a micromirror array, and a microlens array, and 3D image technology uses a stereoscopic method which creates images in 3 dimensions by means of perception of depth caused by binocular image disparity. However, since both technologies create 3D images with front perception of depth, there are technical limitations such that 3D images are significantly different depending on the viewing angle and it causes fatigue of viewer's eyes and dizziness of viewer.
Currently, it is essential to use microlens arrays appropriately designed for each application in order to implement projections, virtual screens or 3D images similar to actual images on various electronic devices. Passive lens layers with a constant standard have been used depending on their uses. In general, the passive lens layer is manufactured through various methods such as laser guided dry etching, photolithography using diffuser, laser chemical vapor deposition and FIB (focused ion beam) milling, etc. Recently, methods using reflow phenomenon of polymer materials and imprinting using PDMS mold and UV curing polymers are used to simplify the process and reduce cost for manufacturing microlens arrays.
However, such methods have still difficulties in manufacturing microlens array having ensured flexibility and desired material properties and further, since lens factors are fixed, it cannot perform various functions depending on the purpose of a user on a single electronic device.
Conventional technologies relating to a microlens array are described below.
KR Pub No. 10-2009-0033454 discloses a microlens sheeting using a shape memory material. When the sheeting is heated to a temperature above the transition temperature (Tg) of the shape memory material, it is physically deformed in a flat shape.
It is a display apparatus technology controlling a focal distance through lens shape changes. It has some drawbacks such that it is hard to implement in a single layer structure since a shape is deformed by applying heat to a lens layer using a heat applying sheeting; it is difficult to control the focal distance of the lens more than one step since the lens shape is deformed in a flat shape only when the sheeting is heated to a temperature above the transition temperature (Tg); it is difficult to change optical properties of individual lens or a part of the lens on the microlens array; and it has a difficult structure to change optical angle among the optical properties. In addition, since the lens shape is deformed only with heat application, there is limitation in terms of responding rate of the lens when heat transfer rate is considered.
KR Pub. No. 10-2008-0043610 discloses a method forming microlens by placing a mixture of a polymer and a liquid crystal on the display panel where images are displayed and arranging the mixture according to electric signals.
Even though various shapes of lenses which provide 3D images can be prepared by varying arrangements of the mixture of the polymer and the liquid crystal according to electric signals, dynamic control in a lens shape which is prepared during the process is not possible since the polymer becomes hardened due to UV irradiation, and 2D/3D display conversion becomes difficult.
KR Pub. No. 10-2011-0118731 discloses a method for manufacturing a microlens array which is protruded in a hemispherical shape from a surface, the method including a resist layer forming process, a reflow process and an etching process using a mixed gas of hydrogen-containing molecules and fluorine-containing molecules. It allows easy control in height of the microlens during the manufacturing process to improve a light collection efficiency and satisfy various requirements.
However, it also has a drawback such that it does not allow dynamic control in a lens shape produced during the manufacturing process, resulting in difficulties in appropriate changes of lens factors.